1. Field of the Invention
The present invention relates to a method of scheduling a shared channel of a wireless packet communication system, and more particularly, to a shared scheduler of a wireless packet communication.
2. Discussion of the Related Art
In a current 1xCDMA system, it is designed to support voice services of a circuit switched mode and low data services. As the demand of wireless Internet services has been increased, a new communication tool for only high-data packet, called HDR (High Data Rate) or 1x-EV DO (1x-Evolution Data Only), was suggested. This HDR or 1 xEV-DO is specifically designed for high speed packet data service other than voice service and offers a bandwidth efficiency for data traffic that is 3 to 4 times greater than the current 1xCDMA system. This technology is ideal for high-speed mobile as well as Fixed wireless Internet services.
Besides, there exists another new air interface technology is called 1x-EV-DV (1x-Evolution Data and Voice) evolved from 1x-EV DO. The 1x-EV-DV is capable of providing both high-rate packet data service and voice services of circuit switched mode at the same time. Moreover the 1x-EV-DV put forward a system whose voice modes are fully compatible with the current 1xCDMA voice modes, and shared channel services such as 1x-EV-DO for enhanced data services. In order for the compatibilities of the current 1xCDMA2000, the 1x-EV-DV, reusing all common channels from CDMA 2000, supports Radio Configuration (hereafter referred to RC). In addition, it is also composed of shared-channels for packet data services as independent RC formats.
In case of existing voice service user and data service user using the circuit switched mode, the 1x-EV-DV system dynamically allocates the remaining power and walsh code for Forward Packet Data Channel and the 1x-EV-DV system increases data throughputs of a base station by allocating the remaining power from the base station and walsh codes to the prioritized users (terminals or handsets of cellular) who's had a better link channel quality from the base station to users. However the base station does not know what the forward link channel quality is to an individual user without feedback information from the user. Once the feedback system is set up, the user (the terminal of cellular) transmits data to let the base station know about the link channel quality. And based on the feedback information, it requires to schedule a sequence of data to be transmitted to the target terminals for prioritized users. In this case it is necessary to select an appropriate method of a modulation and polarizations of the channels for the feedback system successfully to transmit such an information containing the link channel quality, which is called transmitting scheduling.
Hereinbelow, a method of measuring the quality of a forward link channel is described. Assuming that the terminal measured values of C/I (ratio of carrier signal to interference) in a common pilot, the measured values become quantized and sent back to the base station through reverse link channels. That is, by the above method, the terminal itself can select the base station or sectors which has the best link channel quality. Once the selection is done, values of the link channel quality selected by the terminal are transmitted to the selected base station or sector.
In other words, the terminal selects which base station has the best channel quality and then let the selected base station know what the best channel quality. This process is done through RCQICH (Reverse Common Quality Indicator Channel) to transmit the information back to the base station or sector. Therefore only a base station received the information of the link channel quality knows which terminal is selected. Then the base station starts to transmit data based on the received information of the link channel quality.
In the 1x-EV-DV system, multiple terminals transmit data through one shared-channel without causing any jam in data processing. In order to do that, it requires an algorithm to share resources with the multiple terminals. By this algorithm, the shared-channel is allocated to each terminal out of the multiples. Which is done efficiently by a role of a scheduler.
The primary role of the scheduler is to increase the system throughput and simultaneously allocate the resources to each terminal properly. In general to maximize the system throughput, the most resources are allocated to the terminals having maximum values of C/I (ratio of carrier signal to interference). However a problem comes up when the above algorithm is implemented. What the problem is that few terminals having higher values of C/I monopolize all the resources, which results in the majority of target terminals losing all the link abilities.
To overcome this hindrance, the chance of transmitting data could be equally given to all the multiple target terminals. But unfortunately it causes another problem such as worsening the system throughput efficiency, even though solving the problem of abandoning the majority of target terminals. Eventually it is necessary to implement an alternative algorithm which can trade off between the system throughput efficiency and the resource allocation to selected terminals.
Assuming the current HDR system being implemented, the scheduling algorithm is known to meet the following equation below:P(k)=DRC(k)/Throughput for k_th MS  (1)
Wherein DRC(k) is the data rate of k_th ordinal number of the terminal, Throughput for K_th MS is the throughput of k_th terminal to the base station, and P(k) is priority function to prioritize k_th ordinal number of the terminal.
According to the equation (1), the terminal having the maximum value of the priority function receive the allocation of time slots and then starts to transmit packet data to the base station. This is called a proportional fair scheduler.
By considering the 1x-EV-DV system, the information of channel conditions transmitted by the terminals is formatted as the ratio of signal carrier to interference (C/I). Compared to HDR that transmitting, data rate is selected by the terminal itself, the base station of 1x-EV-DV system receives C/I transmitted from the terminals. Then based on the C/I indicating the channel conditions, the base station selects the transmitting data rate other than the terminals.
According to the 1x-EV-DO using C/I to indicate the channel conditions, two terminals having 4 dB and 7 dB of C/I, for example, should have different link availabilities. Even though these two terminals receive the same transmitting data rates, the terminal having 7 dB for C/I evidently have lower error rate of transmitted packets than the other with 4 dB. Consequently regardless of equal transmitting data rates, the scheduler must allocate more time slots to the terminal having higher values of C/I in order to increase the system throughput efficiency. Since the PF scheduler gives the equal priorities on the terminals having same transmitting data rates, it makes a worse as far as the system throughput efficiency is concerned
Furthermore the PF scheduler is not able to prioritize the individual terminal grade and provided service type at all. For instance, it is desirable for a terminal requiring real-time services, such as image data, to have a higher priority to transmit data packets than others for better link services. Unfortunately the PF scheduler is unable to meet this prioritized services and even could not guarantee the link channel quality due to the fact that the PF scheduler does not recognize which service such as FTP or real-time service has higher priorities terminal.